Object-Oriented Modeling
Using UML
CS 3331
Sections 2.1 and 2.2
Chapter 5 of UML@Classroom (Martina Seidl, et al.,
Springer 2015; ebook)
Outline

State machine diagram
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Basic elements
Protocol vs behavior state machines
Structuring state machines
Sequence diagram
2
Dynamic Models
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
Used to model control aspects (e.g.,
when)
Several different models possible, e.g.,

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State machine diagram: focusing on state
changes
Interaction diagram: focusing on interactions
Sequence diagram: time order of interactions
between objects
 Communication diagram: messages passed
between objects

3
State Machine Diagram

Depicts the flow of control using states and
transitions by describing
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Generalization of finite state machines
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How an object or system changes over time
Event (e.g., operation calls) it may respond to
How it respond to them
Capture state-dependent behavior precisely
Good for modeling reactive systems

Passive nature (vs active)
4
Modeling Object States


Graph representing finite state machine
Network of states and transitions
button pressed
On
Off
button pressed
5
Elements of State Machine
Diagram
Final state
Initial state
Transition
Running
Idle
State
6
State

Condition or situation in the life of a system (or
object) during which it:
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


Satisfies some condition,
Performs some activity, or
Waits for some events.
Set of values of properties that affect the
behavior of the system (or object).



Abstraction over object’s concrete fields
Determines response to an event,
Thus, different states may produce different
responses to the same event
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State (Cont.)

Examples
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The invoice is paid.
The car is parked.
The engine is running.
Kate is working.
Jim is playing.
All ships are placed.
A Game is over.
The system is waiting for a player’s move.
8
Transition

Relationship between two states indicating that
a system (or object) in the first state will:



Perform certain actions and
Enter the second state when specified event occurs
and specified condition is satisfied.
Consists of:
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
Source and target states
Optional event, guard condition, and action
Event [Condition] / Action
Source
Target
9
Definition

Event

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
Action

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
An occurrence of a stimulus that can trigger a state
transition
Instantaneous and no duration
An executable atomic computation that results in a
change in state of the model or the return of a value
Run to completion
Guard

Side condition enabling/preventing a transition
keyPressed(k) [k == ENTER_KEY] / buf := input
10
Example
pressed/turn on light
Off
On
pressed/turn off light
Q: Model a night light that automatically turns on and off?
11
Outline

State machine diagram




Basic elements
Protocol vs behavior state machines
Structuring state machines
Sequence diagram
12
Protocol vs. Behavior Machines

Protocol state machine

Specifies the intended pattern of calls on an object by
specifying





which operations of the object can be called in which state
and under which condition, thus specifying the allowed call
sequences on the object's operations.
Describes an object's life cycle.
Post-conditions are used instead of actions
Behavior state machine



Expresses the behavior of part of a system, e.g., to define
object and operation behavior
Actions are used instead of post-conditions
States can have actions (entry, exit, do)
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Protocol State Machine
Account
deposit(x)
-balance: int
+ withdraw(x: int): void
+ deposit(x: int): void
Not Overdrawn
[balance >= 0]
withdraw(x)[balance - x < 0]
deposit(x)[balance + x >= 0]
withdraw(x)[balance - x >= 0]
Overdrawn
[balance < 0]
deposit(x)[balance + x < 0]
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Behavior State Machine
[i < N && a[i] != v] / i := i + 1
/ k := -1; i = 0
Searching
[i <= N && a[i] != v]
[a[i] = v] / k := i
[i >= N && a[i] != v]
15
In Class: Digital Watch

(Pairs) Draw a state machine diagram
The watch has a single mode button and a single
advance button. Pressing the mode button once
and then pressing the advance button increments
the hours by 1. Each press of the advance button
increments the hour. Pressing the mode button the
second time allows advancing the minutes by one.
Pressing the mode button a third time displays the
current time. While displaying the current time, the
advance button is ignored. Pressing the mode
button allows the user to set the hour again.
16
More on States

Optional internal activities
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Actions and activities performed while in the state
Action vs activity: atomic vs interrupt-able
Predefined: entry, exit, do
Optional internal transitions

Reaction within a state but without changing state
Name
Internal activities
Internal transitions
17
Internal Activities and Transitions

Internal actions/activities

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Entry: action performed on entry to state
Exit: action performed on exit from state
Do: activity performed while in the state
Internal transitions

Reactions to events that doesn’t cause state changes
Attacking
entry/unsheathe sword
do/charge
exit/sheathe sword
enemy swings[distance<3 ft]/dodge
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Example
[number.isValid()]
Starting
entry / start dial tone
exit / end dial tone
dialed (n)
Dialing
entry / number.append(n)
dialed (n)
19
Outline

State machine diagram




Basic elements
Protocol vs behavior state machines
Structuring state machines
Sequence diagram
20
Structuring Diagrams
Can this diagram be presented better?
recovery success
recovery failure
anomaly
Recovery
Identification
Normal
temperature
pressure
recovery
failure
recovery
success
Pressure
Recovery
Temperature
Recovery
recovery
failure
recovery success
21
Composite States
anomaly
Recovery
Normal
recovery
success
recovery
failure
22
Composite States (Cont.)
anomaly
Recovery
Recovery
Identification
Normal
recovery
success
recovery
failure
pressure
Pressure
Recovery
temperature
Temperature
Recovery
23
Composite States (Cont.)
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Used to simplify diagrams
Inside, looks like state machine diagram
May have composite transitions
May have transitions from substates
Sequential (OR) and parallel (AND) states
24
Composites and Transitions
Transition to/from composite state
Active
Idle
Validating
Selecting
Processing
Maintenance
Printing
Transition from substate
25
Exercise

Model a night light that


Automatically turns on and off when it becomes
dark or bright.
Has a button to select a light color: white, blue,
and red. The initial color is white, and pressing
the button while the light is on changes it to the
next color.
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Parallel Composition


Concurrency (split of control)
Synchronization
Superstate
substate1
substate2
substate3
substate4
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Example
28
Exercise

Model a night light that


Automatically turns on and off when it becomes
dark or bright.
Has a button to select a light color: white, blue,
and red. The initial color is white, and pressing
the button changes it to the next color in the
color sequence. The button works regardless
whether the light is on or off.
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Outline


State machine diagram
Sequence diagram
30
Sequence Diagram


Describes a sequence of method calls
among objects
Highlights the time ordering of method
calls
31
Example
: Cus tom er
object
: Order
: Paym ent
: Product
: Supplier
place an order
proces s
control
lifetime
validate
if ( paym ent ok )
deliver
if ( not in s tock )
back order
get addres s
m ail to addres s
message
32
Example (Cont.)
: Cus tom er
: Order
: Paym ent
: Product
: Supplier
place an order
proces s
validate
Sequence of message sending
if ( paym ent ok )
deliver
if ( not in s tock )
back order
get addres s
m ail to addres s
33